Help with 3D modeling
Create a black and white Displacement Map in image editing software.



Add six Edge Loops CTRL+R. Then select the two inner Edge Loops and Scale them in press S and then SHFT+Z to keep them from moving on the "Z" axis.



Using Cycles create a new material and bring the Displacement Map in to the Image Texture Node (Set this to Non Color Data).



UV Unwrap your bullet using Cylinder Projection. Open your Displacement image then Scale and position the UV Map to fit the image.